Propeller fan

ABSTRACT

Provided is a propeller fan, including: a boss section including a tubular wall; and a plurality of blades extending in a radiate manner from an outer peripheral surface of the tubular wall of the boss section. Secondary flow control slits are each formed between a pair of the adjacent blades on the outer peripheral surface. The slit passes through the tubular wall to communicate between an inside of the boss section and an outside of the boss section. A downstream end of the tubular wall is closed, whereas an upstream end of the tubular wall is open. In side view, the slit extends obliquely to a rotation axis of the propeller fan, and extends obliquely in the same direction as a forming direction of a blade root portion of each of the plurality of blades.

TECHNICAL FIELD

The present invention relates to a propeller fan, an air blower, and an outdoor unit.

BACKGROUND ART

In general, a propeller fan includes a cylindrical boss connected to a driving source, and a plurality of blades extending in a radiate manner from an outer peripheral surface of the boss. Further, in Patent Literature 1, there is disclosed such a configuration that, in each blade, a position at which a camber ratio is maximum is set to a position closer to a blade root portion than an outer peripheral edge of the blade, and the camber ratio is gradually decreased toward the blade root portion from the position at which the camber ratio is maximum. With this configuration, occurrence of a vortex is suppressed without causing the blade to exert a large amount of work in the vicinity of the blade root portion.

CITATION LIST Patent Literature

[PTL 1] JP 2012-052443 A (mainly FIG. 1)

SUMMARY OF INVENTION Technical Problem

By the way, the Coriolis force acting in a direction reverse to a rotating direction of the propeller fan balances with a pressure gradient between adjacent blade surfaces, and thus an air current between the blades flows along the blades. However, the above-mentioned pressure gradient influences up to the outer peripheral surface of the boss, whereas relative velocity of the air current is low in a boundary layer on the outer peripheral surface of the boss, with the result that the Coriolis force is reduced. Accordingly, the above-mentioned balance is lost in the vicinity of the outer peripheral surface of the boss, and due to the influence of the above-mentioned pressure gradient, a secondary flow toward an adjacent blade is generated. The secondary flow collides with the blade, and thus a vortex occurs, which causes noise.

On the other hand, according to the propeller fan disclosed in Patent Literature 1, the camber ratio is gradually decreased toward the blade root portion from the position at which the camber ratio is maximum, thereby being capable of suppressing a vortex, which may occur at a connecting portion between the blade and the boss. However, there is a problem in that an amount of work of the blade is reduced in the vicinity of the connecting portion between the blade and the boss.

The present invention has been made in view of the above, and has an object to provide a propeller fan capable of suppressing a vortex, which may occur at a connecting portion between a blade and a boss, thereby reducing a noise level of the fan without depending on setting of a camber ratio of the blade in the vicinity of a blade root portion.

Solution to Problem

In order to attain the above-mentioned object, according to one embodiment of the present invention, there is provided a propeller fan, including: a boss section including a tubular wall; and a plurality of blades extending in a radiate manner from an outer peripheral surface of the tubular wall of the boss section. Secondary flow control slits are each formed between a pair of the adjacent blades on the outer peripheral surface. Each of a plurality of the secondary flow control slits passes through the tubular wall to communicate between an inside of the boss section and an outside of the boss section. A downstream end of the tubular wall is closed, whereas an upstream end of the tubular wall is open. In side view, the each of the plurality of the secondary flow control slits extends obliquely to a rotation axis of the propeller fan, and extends obliquely in the same direction as a forming direction of a blade root portion of each of the plurality of blades.

In order to attain the object, according to one embodiment of the present invention, there is provided an air blower, including: the above-mentioned propeller fan according to the one embodiment of the present invention; a driving source for applying a driving force to the propeller fan; and a casing in which the propeller fan and the driving source are housed.

Further, in order to attain the object, according to one embodiment of the present invention, there is provided an outdoor unit, including: a heat exchanger; the above-mentioned propeller fan according to the one embodiment of the present invention; a driving source for applying a driving force to the propeller fan; and a casing in which the propeller fan, the driving source, and the heat exchanger are housed.

Advantageous Effects of Invention

In the propeller fan according to the one embodiment of the present invention, it is possible to suppress the vortex, which may occur at the connecting portion between the blade and the boss,thereby reducing the noise level of the fan without depending on the setting of the camber ratio of the blade in the vicinity of the blade root portion.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating a propeller fan according to a first embodiment of the present invention as viewed from a downstream side.

FIG. 2 is a side view illustrating the propeller fan according to the first embodiment.

FIG. 3 is a view illustrating an air current flowing over an outer peripheral surface of a boss of the propeller fan according to the first embodiment.

FIG. 4 is a view illustrating an air current passing through a slit in the outer peripheral surface of the boss of the propeller fan according to the first embodiment.

FIG. 5 is a view illustrating a position of a slit formed in the outer peripheral surface of the boss according to a second embodiment of the present invention.

FIG. 6 is a view illustrating a position of a slit formed in the outer peripheral surface of the boss according to a third embodiment of the present invention.

FIG. 7 is a view illustrating a position of a slit formed in the outer peripheral surface of the boss according to a fourth embodiment of the present invention.

FIG. 8 is a view illustrating a shape of a slit formed in the outer peripheral surface of the boss according to a fifth embodiment of the present invention.

FIG. 9 is a view illustrating a shape of a slit formed in the outer peripheral surface of the boss according to a sixth embodiment of the present invention.

FIG. 10 is a view illustrating an air current passing between blades of a propeller fan according to a comparative example.

FIG. 11 is a perspective view illustrating an outdoor unit according to a seventh embodiment of the present invention as viewed from an air outlet side thereof.

FIG. 12 is a view illustrating a configuration of the outdoor unit according to the seventh embodiment as viewed from a top surface side thereof.

FIG. 13 is a view illustrating a state in which a fan grille is removed according to the seventh embodiment.

FIG. 14 is a view illustrating an internal configuration in a state in which a front panel and the like are further removed according to the seventh embodiment.

DESCRIPTION OF EMBODIMENTS

Now, a propeller fan according to embodiments of the present invention is described with reference to the accompanying drawings. Note that, in the drawings, the same reference symbols represent the same or corresponding parts.

First Embodiment

FIG. 1 is a perspective view illustrating a propeller fan according to a first embodiment of the present invention as viewed from a downstream side. FIGS. 2, 3, and 4 are a side view illustrating the propeller fan, a view illustrating an air current flowing over an outer peripheral surface of a boss, and a view illustrating an air current passing through a slit, respectively. A propeller fan 1 includes a boss section 3 and a plurality of blades 5.

The boss section 3 includes a tubular wall 3 a having a cylindrical shape. An output shaft of a driving source such as a motor is connected to a center portion 3 b of the boss section 3, and the propeller fan 1 is rotated by a driving force of the driving source. Note that, reference symbol RD of FIG. 1 represents a rotating direction of the propeller fan 1, and reference symbol RA of FIG. 2 represents a rotation axis of the propeller fan 1. Reference symbol US conceptually represents an upstream air current, and reference symbol DS conceptually represents a downstream air current.

As illustrated best in FIG. 4, a downstream end of the tubular wall 3 a of the boss section 3 is closed by a lid plate portion 3 c. On the other hand, an upstream end of the tubular wall 3 a of the boss section 3 is open. With this configuration, an inside of the boss section 3 and an outside of the boss section 3 are communicated to each other.

The plurality of blades 5 extend in a radiate manner from an outer peripheral surface 3 d of the tubular wall 3 a of the boss section 3. Further, the plurality of blades 5 have mutually the same shape, and are provided at equal intervals. The blades 5 each include an outer peripheral edge 5 a, a blade root portion 5 b, a leading edge 5 c, a trailing edge 5 d, a positive pressure surface 5 e, and a negative pressure surface 5 f.

The outer peripheral edge 5 a is an edge portion of each blade 5 on a radially outer side thereof, and is also an edge portion extending in a circumferential direction. By contrast, the blade root portion 5 b is a portion of each blade 5 connected to the outer peripheral surface 3 d of the boss section 3. The leading edge 5 c is an edge portion connecting a leading end of the outer peripheral edge 5 a and a leading end of the blade root portion 5 b, and is also an edge portion on a forward side in the rotating direction of the propeller fan 1. Similarly, the trailing edge 5 d is an edge portion connecting a trailing end of the outer peripheral edge 5 a and a trailing end of the blade root portion 5 b, and is also an edge portion on a backward side in the rotating direction of the propeller fan 1. In the illustrated configuration, both the leading edge 5 c and the trailing edge 5 d are curved so as to extend onward in the rotating direction toward the radially outer side.

In plan view, the positive pressure surface 5 e and the negative pressure surface 5 f are each a blade surface defined by the outer peripheral edge 5 a, the blade root portion 5 b, the leading edge 5 c, and the trailing edge 5 d. The positive pressure surface 5 e and the negative pressure surface 5 f are positioned so as to have a mutually front-and-back relationship. The positive pressure surface 5 e is a blade surface on a downstream side of an air current generated through rotation of the propeller fan 1, and the negative pressure surface 5 f is a blade surface on an upstream side of the air current. Further, in the illustrated configuration, the positive pressure surface 5 e is a concave surface concaved toward the downstream side, and the negative pressure surface 5 f is a convex surface convexed toward the upstream side.

Secondary flow control slits 7 are each formed between a pair of adjacent blades 5 on the outer peripheral surface 3 d of the boss section 3. As illustrated best in FIG. 4, each of the plurality of secondary flow control slits 7 in the entire outer peripheral surface 3 d of the boss section 3 passes through the tubular wall 3 a of the boss section 3 to communicate between the inside of the boss section 3 and the outside of the boss section 3.

Further, as illustrated best in FIG. 2, in side view, each of the plurality of secondary flow control slits 7 extends obliquely to the rotation axis RA of the propeller fan, and extends obliquely in the same direction as a forming direction of the blade root portion 5 b of each of the plurality of blades 5. In the illustrated configuration, each of the secondary flow control slits 7 extends straight in side view, and is inclined so that a forward portion thereof in the rotating direction of the propeller fan is positioned on the upstream side of the air current.

Next, air-blowing operation of the propeller fan according to the first embodiment is described. First, with reference to FIG. 10, description is made of a flow in a propeller fan according to a comparative example, which does not have a feature of the present invention. At a radial center portion of each blade 55, as indicated by the arrow F3, an air current flowing into the propeller fan from the upstream side flows along the blade 55 to the downstream side. On the other hand, on an outer peripheral surface of a boss section 53, as indicated by the arrow F4, an air current flowing into the propeller fan from the upstream side flows from the vicinity of a leading edge 55 c of a positive pressure surface 55 e of the blade 55 toward a negative pressure surface 55 f of an adjacent blade 55, and then flows to the downstream side while forming a vortex.

That is, at a radial center portion between the blades, the Coriolis force acting in a direction reverse to the rotating direction balances with a pressure gradient from the positive pressure surface 55 e of the blade 55 to the negative pressure surface 55 f of the adjacent blade 55, and thus the air current between the blades 55 is formed into a flow along the blades 55. However, the above-mentioned pressure gradient influences up to the outer peripheral surface of the boss section 53, whereas relative velocity of the air current is low in a boundary layer on the outer peripheral surface of the boss section 53, with the result that the Coriolis force is reduced. Accordingly, due to the influence of the above-mentioned pressure gradient, a secondary flow toward the negative pressure surface of the adjacent blade is generated. The secondary flow collides with the negative pressure surface, and thus a vortex occurs.

In contrast, in the first embodiment, an upstream end surface of the boss section 3 is open, and the inside of the boss section 3 is communicated to the upstream side of the propeller fan 1. In the outer peripheral surface of the boss section 3, the secondary flow control slit 7 connecting the inside and the outside of the boss section 3 is formed across a region between the blades. Accordingly, in a case where pressure in the region between the blades is higher than pressure in the inside of the boss section 3, as indicated by the solid arrow F1 of FIGS. 3 and 4, the secondary flow is sucked into the inside of the boss section 3 through the secondary flow control slit 7 formed in the outer peripheral surface 3 d of the boss section 3. The secondary flow is sucked into the inside of the boss section 3, and hence the air current flowing toward the negative pressure surface 5 f can be suppressed. Thus, it is possible to suppress turbulence of the air current, which maybe caused by occurrence of a vortex. Conversely, in a case where the pressure in the region between the blades is lower than the pressure in the inside of the boss section 3, as indicated by the dotted arrow F2 of FIGS. 3 and 4, such an air current is generated as to flow out from the inside of the boss section 3 to the outside of the boss section 3 through the secondary flow control slit 7 formed in the outer peripheral surface 3 d of the boss section 3. Due to the above-mentioned air current, the secondary flow is separated from the boundary layer on the outer peripheral surface 3 d of the boss section 3, and hence the air current flowing toward the negative pressure surface 5 f can be suppressed. Accordingly, it is possible to suppress turbulence of the air current, which may be caused by occurrence of a vortex.

Further, with respect to the rotation axis RA of the propeller fan, the secondary flow control slit 7 is inclined in the same direction as a direction of inclination of the blades 5. Hence, the secondary flow control slit 7 can exert a reduced action on the air current parallel to the blades 5. In addition, the secondary flow control slit 7 is orthogonal to the secondary flow, thereby being capable of increasing the above-mentioned effect of suppressing occurrence of a vortex.

As described above, according to the propeller fan of the first embodiment, the secondary flow control slit suppresses a vortex, which may occur at a connecting portion between the blade and the boss, thereby being capable of reducing the noise level of the fan. Further, this configuration does not depend on setting of a camber ratio of the blade in the vicinity of the blade root portion, thereby being capable of suppressing occurrence of a vortex while causing the blade to effectively work on a region up to the vicinity of the blade root portion.

Second Embodiment

FIG. 5 is a view illustrating a position of a slit formed in the outer peripheral surface of the boss according to a second embodiment of the present invention. FIG. 5 illustrates a partial developed state of the outer peripheral surface 3 d of the boss section 3. FIG. 5 illustrates the blade root portions 5 b of the pair of blades 5 and a secondary flow control slit 107 positioned between the blade root portions 5 b.

In FIG. 5, an imaginary line VL1 connecting the plurality of leading edges 5 c at positions of the blade root portions 5 b, and an imaginary line VL2 connecting the plurality of trailing edges 5 d at positions of the blade root portions 5 b are assumed. In the second embodiment, the secondary flow control slit 107 is formed in a range between the imaginary line VL1 and the imaginary line VL2. Note that, the other features of the secondary flow control slit 107 may be the same as those of the above-mentioned secondary flow control slit 7 according to the first embodiment.

Also in the second embodiment, similarly to the above-mentioned first embodiment, it is possible to suppress a vortex, which may occur at the connecting portion between the blade and the boss, thereby being capable of reducing the noise level of the fan. In particular, in the second embodiment, the secondary flow control slit is limitedly formed in a range in which the pressure gradient between the blades is large and the secondary flow is easily generated, and hence it is possible to suppress occurrence of a vortex while reducing an influence on a primary flow.

Third Embodiment

FIG. 6 is a view illustrating a position of a slit formed in the outer peripheral surface of the boss according to a third embodiment of the present invention, and is also a view similar to FIG. 5. In FIG. 6, in addition to the same imaginary lines VL1 and VL2 as those of FIG. 5, an imaginary line VL3 is assumed. The imaginary line VL3 extends along an intermediate position between the pair of adjacent blades (blade root portions 5 b) in a circumferential direction. More specifically, the imaginary line VL3 is a line obtained by aligning, from a pair of leading edges to a pair of trailing edges, circumferential middle points between a pair of camber lines (blade thickness center lines) CL of the pair of adjacent blades.

In the third embodiment, a secondary flow control slit 207 extends in a range between the imaginary line VL1 and the imaginary line VL2, and is arranged in a forward region in the rotating direction RD of the propeller fan with respect to the imaginary line VL3. Note that, the other features of the secondary flow control slit 207 may be the same as those of the above-mentioned secondary flow control slit 7 according to the first embodiment.

Also in the third embodiment, the same advantage as that of the above-mentioned second embodiment can be obtained. In addition, in the third embodiment, the secondary flow control slit 207 is formed at a position closer to the negative pressure surface 5 f where the secondary flow becomes strongest (that is, a position closer to the negative pressure surface 5 f than the positive pressure surface 5 e), and hence an effect of suppressing the secondary flow can be significantly obtained.

Fourth Embodiment

FIG. 7 is a view illustrating a position of a slit formed in the outer peripheral surface of the boss according to a fourth embodiment of the present invention, and is also a view similar to FIG. 5. In FIG. 7, in addition to the same imaginary lines VL1, VL2, and VL3 as those of FIG. 6, imaginary lines VL4 and VL5 are assumed.

First, with reference to FIG. 7, the imaginary line VL4 is a line positioned at equal distances from the pair of imaginary lines VL1 and VL2. In other words, the imaginary line VL4 is a line extending along an intermediate position between the pair of imaginary lines VL1 and VL2 in a direction of the rotation axis of the propeller fan. Further, when, in FIG. 7, P represents an intersection point between the imaginary line VL4 and the camber line (blade thickness center line) CL of the forward blade 5 of the pair of corresponding blades 5 in the rotating direction RD of the propeller fan, a line segment joining the leading edge 5 c of the corresponding backward blade 5 and the intersection point P on the corresponding forward blade 5 is assumed as the imaginary line VL5.

Further, in the fourth embodiment, a secondary flow control slit 307 extends in the range between the imaginary line VL1 and the imaginary line VL2, and is arranged in the forward region in the rotating direction RD of the propeller fan with respect to the imaginary line VL3 and in a backward region in the rotating direction RD of the propeller fan with respect to the imaginary line VL5. In other words, with reference to FIG. 7, the secondary flow control slit 307 is arranged in a region surrounded by the imaginary line VL2, the imaginary line VL3, the imaginary line VL5, and the forward blade 5 of the pair of corresponding blades 5 in the rotating direction RD of the propeller fan. Note that, the other features of the secondary flow control slit 207 may be the same as those of the above-mentioned secondary flow control slit 7 according to the first embodiment.

Also in the fourth embodiment, the same advantage as that of the above-mentioned third embodiment can be obtained. In addition, the secondary flow is considerably easily generated in a region ranging from the vicinity of the leading edge of the backward blade connected to the boss section to the vicinity of a midpoint between the leading edge and the trailing edge of the adjacent forward blade or the trailing edge of the adjacent forward blade. In this context, the fourth embodiment has such an advantage that an action exerted by the secondary flow control slit can be obtained more intensively in the region where the secondary flow is considerably easily generated.

Fifth Embodiment

FIG. 8 is a view illustrating a position of a slit formed in the outer peripheral surface of the boss according to a fifth embodiment of the present invention, and is also a view similar to FIG. 5. As illustrated in FIG. 8, a secondary flow control slit 407 according to the fifth embodiment extends in parallel to a camber of the blade 5. In particular, the secondary flow control slit 407 illustrated in FIG. 8 is a limited example of the fifth embodiment. However, in an arrangement mode of the secondary flow control slit according to the above-mentioned fourth embodiment (in FIG. 8, an imaginary line and an intersection point are not shown), the secondary flow control slit 407 is further formed so as to be curved in parallel to the camber of the blade 5. Note that, the secondary flow control slit according to the fifth embodiment corresponds to the secondary flow control slit according to anyone of the above-mentioned first to fourth embodiments, which extends in parallel to the camber of the blade, and is not always limited to the state illustrated in FIG. 8.

Also in the fifth embodiment, at least the same advantage as that of the above-mentioned first embodiment can be obtained. In addition, the secondary flow control slit is parallel also to the primary flow of the air current generated between the blades, and hence it is possible to reduce the influence on the primary flow.

Sixth Embodiment

FIG. 9 is a view illustrating a position of a slit formed in the outer peripheral surface of the boss according to a sixth embodiment of the present invention, and is also a view similar to FIG. 5. As illustrated in FIG. 9, a secondary flow control slit 507 according to the sixth embodiment extends so as to have a width of one tenth or less of a circumferential inter-blade distance L between the pair of corresponding blades 5 (dimension in a direction orthogonal to an extending direction of the slit). Further, the other configurations of the secondary flow control slit 507 are the same as those of the secondary flow control slit according to any one of the above-mentioned first to fifth embodiments.

Also in the sixth embodiment, at least the same advantage as that of the above-mentioned first embodiment can be obtained. Further, it is possible to reduce the influence on the primary flow, which may be caused due to an increased amount of the air current passing through the secondary flow control slit.

Seventh Embodiment

FIG. 11 is a perspective view illustrating an outdoor unit (air blower) according to a seventh embodiment as viewed from an air outlet side thereof, and FIG. 12 is a view illustrating a configuration of the outdoor unit as viewed from a top surface side thereof. Further, FIG. 13 illustrates a state in which a fan grille is removed, and FIG. 14 is a view illustrating an internal configuration in a state in which a front panel and the like are further removed.

As illustrated in FIGS. 11 to 14, an outdoor-unit main body (casing) 51 is formed as a casing including a pair of right and left side surfaces 51 a, 51 c, a front surface 51 b, aback surface 51 d, a top surface 51 e, and a bottom surface 51 f. The side surface 51 a and the back surface 51 d each have an opening portion through which the air is sucked from an outside of the outdoor-unit main body (see the arrows A of FIG. 12). Further, in a front panel 52 of the front surface 51 b, an air outlet 53 is formed as an opening portion through which the air is blown out to the outside (see the arrows A of FIG. 12). In addition, the air outlet 53 is covered with a fan grille 54. This configuration prevents contact between an object, etc. and the propeller fan 1, to thereby assure safety.

The propeller fan 1 is mounted in the outdoor-unit main body 51. The propeller fan 1 is the propeller fan according to any one of the above-mentioned first to sixth embodiments. The propeller fan 1 is connected to a fan motor (driving source) 61 on the back surface 51 d side through intermediation of a rotation shaft 62, and is rotated and driven by the fan motor 61.

An inside of the outdoor-unit main body 51 is partitioned by a partition plate (wall) 51 g into an air-blowing chamber 56 in which the propeller fan 1 is housed and mounted, and a machine chamber 57 in which a compressor 64 and the like are mounted. On the side surface 51 a side and the back surface 51 d side in the air-blowing chamber 56, a heat exchanger 68 extending in substantially an L-shape in plan view is provided.

A bellmouth 63 is arranged on a radially outer side of the propeller fan 1 arranged in the air-blowing chamber 56. The bellmouth 63 is positioned on an outer side of the outer peripheral edge of each of the blades 5, and exhibits an annular shape along the rotating direction of the propeller fan 1. Further, the partition plate 51 g is positioned on one side of the bellmouth 63 (on a right side in the drawing sheet of FIG. 12), and a part of the heat exchanger 68 is positioned on another side (opposite side) thereof (on a left side in the drawing sheet of FIG. 12).

A front end of the bellmouth 63 is connected to the front panel 52 of the outdoor unit so as to surround an outer periphery of the air outlet 53. Note that, the bellmouth 63 may be formed integrally with the front panel 52, or may be prepared as a separate component to be connected to the front panel 52. Due to the bellmouth 63, a flow passage between an air inlet side and an air outlet side of the bellmouth 63 is formed as an air passage in the vicinity of the air outlet 53. That is, the air passage in the vicinity of the air outlet 3 is partitioned by the bellmouth 63 from another space in the air-blowing chamber 56.

The heat exchanger 68 provided on the air inlet side of the propeller fan 1 includes a plurality of fins aligned side by side so that respective plate-like surfaces are parallel to each other, and heat-transfer pipes passing through the respective fins in an aligning direction of the fins. A refrigerant, which circulates through a refrigerant circuit, flows in the heat-transfer pipes. In the heat exchanger 68 according to this embodiment, the heat-transfer pipes extend in an L-shape along the side surface 51 a and the back surface 51 d of the outdoor-unit main body 51, and as illustrated in FIG. 14, the heat-transfer pipes in a plurality of tiers are configured so as to pass through the fins in a zigzag manner. Further, the heat exchanger 68 is connected to the compressor 64 through piping 65 or the like. In addition, the heat exchanger 68 is connected to an indoor-side heat exchanger, an expansion valve, and the like (not shown) so as to form a refrigerant circuit of an air conditioner. Further, a board box 66 is arranged in the machine chamber 7. Devices mounted in the outdoor unit are controlled by a control board 67 provided in the board box 66.

Also in the seventh embodiment, the same advantage as that of each of the above-mentioned corresponding first to sixth embodiments can be obtained.

Note that, in the seventh embodiment, the outdoor unit of the air conditioner is exemplified as an outdoor unit including an air blower. However, the present invention is not limited thereto, but can be implemented as, for example, an outdoor unit of a hot-water supply device or the like. In addition, the present invention can be widely employed as an apparatus for blowing the air, and can be applied to an apparatus, equipment, and the like other than the outdoor unit.

Although the details of the present invention are specifically described above with reference to the preferred embodiments, it is apparent that persons skilled in the art may adopt various modifications based on the basic technical concepts and teachings of the present invention. Note that, the present invention is widely applicable to, for example, outdoor units of an air blower, an air conditioner, a hot-water supply device, and the like, and to a heat exchanger of a refrigerating cycle.

REFERENCE SIGNS LIST

1 propeller fan, 3 boss section, 3 a tubular wall, 3 d outer peripheral surface, 5 blade, 7, 107,207, 307, 407, 507 secondary flow control slit, 51 outdoor-unit main body (casing), 61 fan motor (driving source), 68 heat exchanger 

1. A propeller fan, comprising: a boss comprising a tubular wall; and a plurality of blades being provided on an outer peripheral surface of the tubular wall of the boss, wherein a slit is formed on the outer peripheral surface, wherein each of a plurality of the slits passes through the tubular wall to communicate between an inside of the boss and an outside of the boss, wherein a downstream end of the tubular wall is closed, whereas an upstream end of the tubular wall is open, and wherein, in side view, the each of the plurality of the slits extends obliquely in the same direction as a forming direction of a blade root of each of the plurality of blades.
 2. A propeller fan according to claim 1, wherein, assuming that VL1 represents an imaginary line connecting a plurality of leading edges at positions of the blade roots of the blades, and VL2 represents an imaginary line connecting a plurality of trailing edges, the slit is formed in a range between the imaginary line VL1 and the imaginary line VL2.
 3. A propeller fan according to claim 2, wherein, assuming that VL3 represents an imaginary line extending along an intermediate position between the pair of the adjacent blades, the slit is arranged in a forward region in a rotating direction of the propeller fan with respect to the imaginary line VL3.
 4. A propeller fan according to claim 3, wherein, assuming that a line positioned at equal distances from the pair of imaginary lines VL1 and VL2 is represented as an imaginary line VL4, and that when P represents an intersection point between the imaginary line VL4 and a camber line of the forward blade of a pair of the corresponding blades in the rotating direction of the propeller fan, a line segment joining a leading edge of a corresponding backward blade and the intersection point P on the corresponding forward blade is represented as an imaginary line VL5, slit is arranged in a backward region in the rotating direction of the propeller fan with respect to the imaginary line VL5.
 5. A propeller fan according to claim 1, wherein the slit extends in parallel to a camber of the blades.
 6. A propeller fan according to claim 1, wherein the slit has a width of one tenth or less of a circumferential distance (L) between the pair of the corresponding blades.
 7. An air blower, comprising: the propeller fan of claim 1; a driving source for applying a driving force to the propeller fan; and a casing in which the propeller fan and the driving source are housed.
 8. An outdoor unit, comprising: a heat exchanger; the propeller fan of claim 1; a driving source for applying a driving force to the propeller fan; and a casing in which the propeller fan, the driving source, and the heat exchanger are housed. 